Nice bat buddy
Looking great again bud!
From what I could imagine from your description, a raw handled cleft has that shape already , the shape will form by shortening the edges of that cleft and gradually removing the wood towards the spine making the spine meet the handle gradually but I am not sure if that would take off much weight off the cleft. Certainly requires special cleft to create such bat in a relatively lighter weight ( around 2.12).
The spine would start from the toe in a straight angled line and reach it's maxium around 5 inches from the toe, then it will stay straight horizontal for whole of the middle and then again gradually goes down to meet the handle.
Apart from concaving.. you also want the spine to meet the toe gradually from 5 inches bottom?